Oxidative dehydrogenation catalyst and process of preparation thereof

ABSTRACT

Oxidative dehydrogenation of organic compounds is carried out in the presence of a potassium/iron/phosphorus/oxygen catalyst composition. A method of preparing the catalyst composition comprising associating potassium with iron and subsequently associating the potassium-iron composite with phosphorus.

States Patent [1 1 Cichowski Jan. 28, 1975 OXIDATIVE DEHYDROGENATIONCATALYST AND PROCESS OF [56] References Cited PREPARATION THERE UNITEDSTATES PATENTS i 1 lnvemorl clchowskh Luis 2.870128 1/1959 Armstrong252/437 x rsp C f- 3.341820 9/1967 Bludcl' 252/435 x [73] Assignee:Phillips Petroleum Company.

' Bartlesville, Okla; Irimury livuminer-H. Snccd [22] Filed: July 20,1973 [57] ABSTRACT [21] Appl. N0.: 381,019 b Oxidative dehydrogenationoi organic compounds is Related Appllcmlon Data carried out in thepresence of a potassium/iron/phos- [62] Division of Ser. No. 109,010,Jan. 22, 1971. Pat. No. phorus/oxygen catalyst composition. A method ofpreparing the catalyst composition comprising associating potassium withiron and subsequently associating the CL 35, 252/ 3 6 E potassium-ironcomposite with phosphorus. [51] Int. Cl B0lj 11/82 I i 58 Field ofSearch 252/435, 437 9 Harms, Nn Drawings OXIDATIVE DEHYDROGENATIONCATALYST AND PROCESS OF PREPARATION THEREOF This application is adivision of copending application Ser. No. 109,010, filed on Jan. 22,1971, now U.S. Pat. No. 3,766,191.

. FIELD OF INVENTION This invention relates to an oxidativedehydrogenation catalyst, a catalytic oxidative dehydrogenation process,and a method of making an oxidative dehydrogenation catalyst.

DESCRIPTION OF PRIOR ART Thermal dehydrogenation of organic compounds,well known in the art, frequently causes undesirable side reactions andsignificantly reduces end product se- 'ganic compositions of significantvalue to the chemical industry.

It is an object of this invention to catalytically oxydehydrogenateorganic compounds under process conditions which yield minimal sidereactions, maximal conversion rates and maximal end product selectivity.

SUMMARY OF INVENTION According to this invention improved oxidativedehydrogenation catalysts containing potassium/iron/phosphorus andoxygen are produced when potassium is associated with iron prior toincorporating the phosphorus.

In one embodiment of this invention it has been found that an improvedpotassium/iron/phosphorusloxygen oxidative dehydrogenation catalyst isprepared in accordance with the following sequence: (1) intimatelymixing a potassium compound with an iron compound, (2) calcining thepotassium/iron mixture, (3) intimately mixing the calcinedpotassium/iron composition with a phosphorus compound and thereafter (4)calcining the potassium/iron/phosphoruscontaining composite.

(l) The first step comprises contacting and intimately mixing a suitableamount ofan oxide of potassium or a compound convertible to potassiumoxide on calcination with a suitable amount of an oxide of iron or acompound convertible to iron oxide on calcination. The term calcination"as used herein is used to describe broadly the heating of any substance,such as an element, compound, composite, composition, a catalyst ormixtures thereof to an elevated temperature in the presence of anoxygen-containing gas, such as air.

Compounds convertible to an oxide of potassium under calciningconditions are exemplified by the following compounds: (a) inorganicpotassium compounds such as potassium hydroxide, potassium nitrate;

potassium nitrite. potassium carbonate, potassium bicarbonate, potassiumeyanate; and (b) organic potassium compounds such as potassium oleate,potassium oxalate, potassium phenolate, potassium phthalate, potassiumsalicylate, potassium succinate, potassium tartrate, potassium acetate,and the like.

Compounds convertible to an oxide of iron under calcining conditions areexemplified by the following compounds: (a) inorganic iron compoundssuch as iron carbonate, iron hydroxide, iron nitrate, iron nitride, and(b) organic iron compounds such as iron acetate. iron formate, ironoleate, iron oxalate, iron phenolate, iron stearate and the like.

The means chosen to prepare mixtures of potassium and iron is notlimiting upon the present invention. Convenient methods of preparingintimate mixtures of potassium and iron are (a) dry mixing powderedcompounds ofthe potassium and iron, or (b) wet mixing solutions ordispersions of potassium and iron compounds. Preferentially, prior tocalcination the mixtures are dried and volatile solvents are removed.

In the preparation of potassium/iron compositions, the potassium contentby weight and the iron content by weight are within the weight ratiorange of from about 0.005:l to ().l5:l. Prcferentially, optimum re sultsare obtained wherein the weight ratio range of potassium to iron is fromabout 0.0l:l to 0.05:].

(2) The second step comprises calcination of the potassium/iron mixtureshaving the weight ratios specified in step 1) above at an elevatedtemperature range of from about l,600F to about 2,000F for O.l-30 hours.

In theory, not to be construed as limiting the scope of this invention,it is believed that the combination of potassium and iron undercalcining conditions causes the formation of at least some quantity of apotassium ferrite compound having a beta-alumina structure, i.e., KFe O(also written as K O.ll IFe O It is presently believed that thisbeta-alumina structure is necessary in order to satisfactorilyincorporate the potassium into the catalyst compositions of thisinvention.

(3) The third step comprises association of the calcined potassium/-ironcomposition with a sufficient quantity of a suitablephosphorus-containing compound to provide a phosphorus content of from 1to 5 times, preferably l to 2 times, the stoichiometric amountrequired'to react with all of the iron in the form of phosphate ions(POf Preferably, the phosphorus content of the calcinedpotassium[iron/phosphorus composite is higher than that calculated foran iron compound containing only phosphate ions. The stoichiometricamount of phosphorus in relation to iron, computed as ferric phosphate,FePO is one atom of phosphorus per atom of iron, and is 20.5 percent byweight phosphorus based on the weight of FePO Examplary forms ofsuitable phosphorus containing compounds include phosphoric acid;phosphorus oxides, such as phosphorus pentoxide; or any compoundconvertible to a phosphorus oxide on calcination. Because of itsconvenient form and ready commercial availability phosphoric acid is apreferred source of phosphorus.

(4) The fourth step after incorporation of phosphorus as specified instep (3) above, comprises calcination of the potassium/iron/phosphoruscomposition in air or an oxygen containing gas at. an elevatedtemperature of about 800F to l,400F for l-25 hours. A calcinationtemperature of about I l0OF to I300F for 2-8 hours is satisfactory inmost instances for the preparation of the catalysts of this invention.

The potassium/iron/phosphorus/oxygen catalysts of this invention can beused in any suitable oxidative dehydrogenation process. Usuallyoperating conditions include a temperature in the range of from about750 to about 1,300F, preferably from 950F to l,lF; a pressure in therange of from about 0.05 to about 250, preferably from 0.1 to 100 psia;a volumetric oxygen- :organic compound feed ratio in the range of fromabout 0.1/1 to about 3/1, preferably from 0.5/1 to 2/1; and, if steam isused, a volumetric steamzorganic feed ratio in the range ofabout 0.1/1to about 100/l preferably /1 to 20/1. Organic compound feed space rates(volumes of organic compound vapor/volume of catalyst/hour, at 32F, 14.7psia) are selected in the range from about 50 to about 5,000, preferablyfrom 100 to about 2,500.

In the broad embodiments of this invention the oxidative dehydrogenationprocesses of this invention include dehydrogenation of variousunsaturated organic compounds that contain at least 3 carbon atoms andat least one grouping, i.e., adjacent carbon atoms singularly bonded toeach other and each attached to at least one hydrogen atom. Among theclass of unsaturated organic compounds which can be dehydrogenated bymeans of the novel process of this invention are alkenes, cycloalkenes,alkyl and alkenyl substituted aromatic compounds, alkyl and alkenylsubstituted pyridine compounds.

Suitable alkene compounds include alkenes having from 3 to carbon atoms,preferably 4 to 6 carbon atoms. Representative alkenes includepropylene, butene-l, butene-2, isobutylene, pentene-l, 2-methylbutene-l, 2-methylbutene-2, 3-methylbutene-l, hexene-l, heptene-l,octene-l, and 2,4,4-trimethylpentene-l and mixtures thereof.

Suitable cycloalkenes include those having from 4 to 10 carbon atomspreferably from 4 to 6 carbon atoms. Representative cycloalkenes includecyclobutene, cyclopentene, cyclohexene, 'cyclooctene,3-isobutylcyclopentene, 3-propylcyclohexene, and the like, and mixturesthereof.

Suitable alkyl and alkenyl substituted aromatic compounds includecompounds containing from 8 to 16 carbon atoms, preferably from 8 to 14carbon atoms. Representative aromatic compounds: include such compoundsas ethylbenzene, propylbenzene, isobutylbenzene,l-methyl-2-propylbenzene, l-butyl-3- hexylbenzene, 'isopropylbenzene,3-phenylcyclopentene-l, '3-ethylbiphenyl, 1,4-diethylbenzene, 4-ethylstyrene, l,2-dimethy1-4-propylbenzene, 2- pentenylbenzene.

Suitable alkyl and alkenyl substituted pyridine compounds includeethylpyridine, 2-methyl-5- ethylpyridine,2,3,4-trimethyl-Sethylpyridine, 2-ethyl-5-hexylpyridine,2-ethylquinoline, 2-pentenyl- 3-acridine.

Preferred unsaturated organic compounds within the scope of thisinvention contain at least 4 carbon atoms which contain a singlegrouping, i.e., adjacent carbon atoms singularly bonded to each otherand each attached to at least one hydrogen atom. Included among thepreferred unsaturated aliphatic. aromatic and hetcrocyclic organiccompounds oxydehydrogcnated in accordance with the process ofthisinvention are Z-methylbutenc-Z, butencl, ethylbenzene. and2-methyI-S-ethyIpyridine.

The molecular oxygen-containing gas employed in the oxydehydrogenationprocesses of this invention can be present as such, or with inertdiluents such as nitrogen. Suitable molecular-oxygen containing gasesinclude air, flue gases containing residual oxygen, andoxygen-containing steam. If desired, pure or substan tially pure oxygencan also be employed.

The oxydehydrogenation process of this invention can be carried out bypassing a feedstock mixture, preferably preheated, of organic compoundover the catalysts of this invention. Recycle of unconverted organiccompound feed and/or steam condensate can be employed if desired;however, the conversion rates and selectivity of this invention aregenerally sufficiently high to eliminate necessity for recycle.

The catalyst of the invention, particularly when steam is used, can beused for long periods without reactivation, however, when and ifreactivation becomes necessary, it can be effected by simply stoppingthe flow of organic feed and allowing the flow of the oxygen containinggases of the feed mixture, such as air and steam, to continue for asuitable reactivation time.

Over prolonged periods of catalytic service, some portion of thephosphorus content of the original K/Fe/P/O composite can be lost with aresultant decrease in catalyst efficiency. To improve catalystefficiency small quantities of phosphorus containing compounds can beintermittently or continuously introduced to the catalyst system. Thephosphorus content of the catalyst system can be maintained at anydesired level by addition of phosphorus to the feedstock. Any loss ofphosphorus can be measured by analysis of the reaction product effluent.Exemplary of compounds which can be employed to add phosphorus to thecatalyst systems include such compounds as phosphoric acid, phosphoruspentoxide, other phosphorus acids and/or anhydrides as well asorgano-substituted phosphines. The form of the phosphorus-containingcompound is not essential nor limiting upon the catalyst systems orprocesses of this invention.

The catalysts of this invention can be employed in many forms and may beprepared by those skilled in the art in the form of granules, pellets,or catalytic forms supported or diluted by silica, alumina, boria,magnesia, titania, zirconia.

1n the following examples the conversion and percentage selectivityvalues were obtained from gas chromotagraph data and the results areshown in mole percent. Accordingly, the selectivity designated is a gasphase value. Small quantities of material remaining in the steamcondensate receiver following the reactor were neglected and are notreported.

EXAMPLE 1 A g quantity of Fe O powder and 9.1 g of K CO were dispersedin distilled water, the water evaporated, and the mixture calcined at1,750F for 24 hours. A 30 g portion of this material, believed tocomprise 1(Fe,, 0 was then treated with 40 cc of 85% H -,PO heated on ahot plate at 200F for minutes, and then cal cined at 1,200F for 4 hours.The catalytic composition was then screened to about a -28 mesh particlesize and was then employed in Example 111.

EXAMPLE H EXAMPLE 111 Catalytic compositions prepared in accordance withExamples l and ll were tested for oxidative dehydrogenation of2-methylbutene-2 to isoprene. The 2 methylbutene-2 was introduced at 400gaseous/hour ly/space/velocity (GHSV), air was introduced at 2,000 GHSV,and steam was introduced at 10,000 GHSV. The reaction was carried out atatmospheric pressure and at a temperature of 1,050F. The results are asfollows:

TABLE I to the oxides on calcination.

2. A method in accordance'with claim 1 wherein a. the potassium and ironare present in a weight ratio in the range of about 0.00511 to about0.15:1.

b. the calcining of said potassium/iron mixture is carried out at atemperature in the range. of about l,600F to about 2,000F,

c. the phosphorus compound is present in an amount in the range of about1 to about 5 times the stoichiometric amount required to react with allthe iron in the form of phosphate ions. and

d. the calcining of said potassiumMon/phosphorus mixture is carried outat a temperature in the range of about 800F to about 1,400F.

3. A method in accordance with claim 1 wherein said potassium compoundis K CO said iron compound is Fe O and said phosphorus compound is H-,PO

8. A method in accordance with claim 1 for preparing an oxidativedehydrogenation catalyst composite which consists essentially ofpotassium, iron, phosphorus, and oxygen, which comprises the sequentialsteps of:

a. contacting, in the absence of phosphorus, a potassium compound withan iron compound, the weight ratio of potassium to iron being in therange of about 0.005:l to about 0.15:1;

b. calcining the thus-contacted potassium compound and iron compound ata temperature within the range of about 1,600F to about 2,000F for aperiod of time in the range of about 0.1 to about hours;

OXlDATlVE DEHYDROGENATION OF ISOAMYLENE TO ISOPRENE (1) Modivity is asimplified selectivity based on gas phase products only. (2] Tested at200, l000, 5000 GHSV for feed, air. steam respectively.

The above data shows that the sequence of steps followed in the catalystpreparation is important. Comparison of Run 1 data with comparison ofRun 3 data illustrates that incorporating the potassium by firstassociating it with the iron and then with the phosphorus gives superiorresults compared with the method of incorporating the potassium byassociating it with a preformed iron phosphate.

What I claim is:

l. A method of preparing a catalyst comprising the following processsequence:

a. contacting a potassium compound and an iron compound in the absenceof phosphorus;

b. calcining the resulting potassium/iron mixture;

c. contacting the thus calcined potassium/iron mixture with a phosphoruscompound; and

d. calcining the resulting potassium/iron/phosphorus mixture; saidpotassium, iron and phosphorus compounds being the oxides or compoundsconvertible c. admixing the thus-calcined composition containingpotassium and iron with a phosphorus-containing compound, the phosphorusof said phosphoruscontaining compound being present in an amount of l to5 times the stoichiometric amount required to react with all of the ironin the form of a phosphate ion; and

d. calcining the resulting admixture containing potassium, iron, andphosphorus at a temperature within the range of about 800F to about1,400F for 21 period of time in the range of about 1 to about 25 hours.

5. A method in accordance with claim 4 wherein said potassium compoundis K CO said iron compound is Fe O and said phosphorus-containingcompound is H PO 6. A catalyst composite which consists essentially ofpotassium, iron, phosphorus, and oxygen, and which is prepared by thesequential steps of:

, 7 s 8 a. contacting, in the absence of phosphorus, a potasoxides oncalcination.

sium compound with an iron compound; 7. A catalyst composite inaccordance with claim 6 b. calcining the thus-contacted potassiumcompound wherein the potassium and iron are present in a weight and ironcompound at a temperature within the ratio in the range of about 0.00511to about 0.l:l and range of about l,600F to about 2,000F for a pe- 5 thephosphorus is present in an amount in the range of riod of time in therange of about 0.1 to about 30 about 1 to about 5 times thestoichiometric amount rehours; quired to react with all the iron in theform of phosc. admixing the thus-calcined composition containing phateions.

potassium and iron with a phosphorus-containing 8. A catalyst compositein accordance with claim 6 compound; and wherein said potassium compoundis K CO said iron d. calcining the resulting admixture containingpotascompound is Fe O and said phosphoruscontaining sium, iron andphosphorus at a temperature within compound is H PO the range of about800F to about l,400F for a pe- 9. A catalyst composite in accordancewith claim 7 riod of time in the range of about l to about 25 whereinsaid potassium compound is K CO said iron hours; compound is Fc O andsaid phosphorus-containing said potassium, iron, and phosphoruscompounds compound is H PO being the oxides or compounds convertible tothe

2. A method in accordance with claim 1 wherein a. the potassium and ironare present in a weight ratio in the range of about 0.005:1 to about0.15:1, b. the calcining of said potassium/iron mixture is carried outat a temperature in the range of about 1,600*F to about 2, 000*F, c. thephosphorus compound is present in an amount in the range of about 1 toabout 5 times the stoichiometric amount required to react with all theiron in the form of phosphate ions, and d. the calcining of saidpotassium/iron/phosphorus mixture is carried out at a temperature in therange of about 800*F to about 1,400*F.
 3. A method in accordance withclaim 1 wherein said potassium compound is K2CO3, said iron compound isFe2O3, and said phosphorus compound is H3PO4.
 4. A method in accordancewith claim 1 for preparing an oxidative dehydrogenation catalystcomposite which consists essentially of potassium, iron, phosphorus, andoxygen, which comprises the sequential steps of: a. contacting, in theabsence of phosphorus, a potassium compound with an iron compound, theweight ratio of potassium to iron being in the range of about 0.005:1 toabout 0.15:1; b. calcining the thus-contacted potassium compound andiron compound at a temperature within the range of about 1,600*F toabout 2,000*F for a period of time in the range of about 0.1 to about 30hours; c. admixing the thus-calcined composition containing potassiumand iron with a phosphorus-containing compound, the phosphorus of saidphosphorus-containing compound being present in an amount of 1 to 5times the stoichiometric amount required to react with all of the ironin the form of a phosphate ion; and d. calcining the resulting admixturecontaining potassium, iron, and phosphorus at a temperature within therange of about 800*F to about 1,400*F for a period of time in the rangeof about 1 to about 25 hours.
 5. A method in accordance with claim 4wherein said potassium compound is K2CO3, said iron compound is Fe2O3,and said phosphorus-containing compound is H3PO4.
 6. A CATALYSTCOMPOSITE WHICH CONSISTS ESSENTIALLY OF POTASSIUM, IRON, PHOSPHORUS, ANDOXYGEN, AND WHICH IS PREPARED BY THE SEQUENTIAL STEPS OF: A. CONTACTING,IN THE ABSENCE OF PHOSPHORUS, A POTASSIUM COMPOUND WITH AN IRONCOMPOUND; B. CALCINING THE THUS-CONTACTED POTASSIUM COMPOUND AND IRONCOMPOUND AT A TEMPERATURE WITHIN THE RANGE OF ABOUT 1,600*F TO ABOUT2,000*F FOR A PERIOD OF TIME IN THE RANGE OF ABOUT 0.1 TO ABOUT 30HOURS; C. ADMIXING THE THUS-CALCINED COMPOSITION CONTAINING POTASSIUMAND IRON WITH A PHOSPHORUS-CONTAINING COMPOUND; AND D. CALCINING THERESULTING ADMIXTURE CONTAINING POTASSIUM, IRON AND PHOSPHORUS AT ATEMPERATURE WITHIN THE RANGE OF ABOUT 800*F TO ABOUT 1,400*F FOR APERIOD OF TIME IN THE RANGE OF ABOUT 1 TO ABOUT 25 HOURS; SAIDPOTASSIUM, IRON, AND PHOSPHORUS COMPOUNDS BEING THE OXIDES OR COMPOUNDSCONVERTIBLE TO THE OXIDES ON CALCINATION.
 7. A catalyst composite inaccordance with claim 6 wherein the potassium and iron are present in aweight ratio in the range of about 0.005:1 to about 0.15:1 and thephosphorus is present in an amount in the range of about 1 to about 5times the stoichiometric amount required to react with all the iron inthe form of phosphate ions.
 8. A catalyst composite in accordance withclaim 6 wherein said potassium compound is K2CO3, said iron compound isFe2O3, and said phosphoruscontaining compound is H3PO4.
 9. A catalystcomposite in accordance with claim 7 wherein said potassium compound isK2CO3, said iron compound is Fe2O3, and said phosphorus-containingcompound is H3PO4.